The present invention relates to the acquisition and processing of measuring data from a group of measuring points (transducers).
Process control requires the plurality of transducers which detect and/or measure specific quantities such as temperature, pressure, flow rates, etc., to be placed in specific locations, and these transducers provide electrical signals representative of these quantities. All these signals must be fed to a suitable signal processing device, for example, a computer facility or the like. It is common practice here to use PCM transmission of the measuring signals to the processing device.
Each signal as generated in a transducer is usually analog-processed at first, such as amplification, normalization, filtering, etc., whereupon the preprocessed signal is digitalized. The digital signals are then transmitted via a common channel and in PCM format to the processor for storage at first and subsequent use.
It is apparent that the initial transducer pickup is, in many instances, a continuous one and if discontinuous this immediate generation of data overlaps usually at random with the operation of the other transducers. Accordingly, the acquisition process requires a certain ordering and sequencing simply because the processor is not in a position to acquire these data completely at random and in complete disregard of overlap.
It is known here to use commutator type interrogation units, being associated with the measuring transducers for cyclically interrogating them. This intermittent, i.e., cyclical interrogation process presupposes that the measurements undertaken by transducer does not change significantly in between sequential interrogations of the same transducer. The interrogation cycle, therefore, must be shorter than the fastest expected data change that must not be missed. This however, means that other transducers are caused to furnish data needlessly frequently. One has, therefore, used several commutators which interrogated different transducers at different frequencies. In cases the commutators are even controlled by a computer as to the specific interrogation instances. In any event, such a system becomes quite complicated and, therefore, is not suitable for many kinds of systems.
Data acquisition systems often cover a wide area as to the distribution of the location of the several transducers. In other words, many of the transducers are far apart from each other and from the central acquisition unit. Attempts to decentralize have been made in that data are preliminarily acquired and then fed via a multi-lined data bus to the central processing station. Such a system as a whole requires a high degree of synchronization of its component or subsystems to insure an orderly and timely flow of data to the central station.
Such a system, however, is not suitable, for example, in aircraft or space vehicles because of space and weight limitations. Moreover, aircraft systems are often subject to restrictive rules, so-called MIL rules, requiring, for example, particular serial data paths between subsystems.
The previously mentioned serially interconnected and decentralized data acquisition system has to work with a high degree of redundency of the information with respect to the several signal paths. This is particularly so because the control information needed in such a system actually reduces the transmission of data per unit time, particularly if the several components are to be accessed basically in a random fashion. Furthermore, such a system is quite extensive as far as the required timing in the serial data bus system and as far as information processing in each subsystem is concerned. There exist systems which exhibit from a system's point of view an optimum in the data acquisition and operation system, but they are deemed excessively expensive and are therefore unsatisfactory.